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At least 235 records · Page 13Linked to original sources
PubMed2000

Dimensional measurement and finite element analysis of I-bar clasps in clinical use.

An I-bar clasp is a popular retainer for distal-extension removable partial dentures. However, there have been almost no evidence-based criteria on the mechanically preferable shape. The present study aimed to investigate the variations of dimension in I-bar clasps used in patients, and to clarify the effect of the variations on stiffness and stress of I-bar clasps by finite element analysis. Dimensions (thickness, width, taper, radius of curvature, length, relation to oral structures) of 23 I-bar clasps were measured. A three-dimensional finite element model was made for each measured I-bar clasp with vertical and horizontal straight sections connected with a curved section. A concentrated load of 5 N was applied at the lowest point of the tip that contacted the abutment in the buccal direction. Maximal equivalent stress and stiffness of each clasp were evaluated. The measured dimension, stiffness, and maximum stress showed wide variations. Mean stiffness was far from the proper one, and mean stress was near the proportional limit of Co-Cr alloy. Considering the stiffness and stresses in this study, only six clasps out of 23 were appropriate. These results suggest that evidence-based criteria of preferable shape of I-bar clasps should be determined.

Dental Clasps↗
PubMed2004

Multicenter evaluation of a new laser guidance system for computed tomography intervention.

PURPOSE: To measure the accuracy of laser-guided punctures and to evaluate the usefulness of the developed laser-guided system. MATERIAL AND METHODS: The study included 67 patients referred for computed-tomography-guided puncture. The majority of the punctured lesions were located in the chest (28 patients) or abdomen (19 patients). The mean diameter of the lesion was 3.1 cm, and the mean path length was 6.8 cm. The laser guide was movable along a horizontal or vertical rail and not physically connected to the CT unit. The angle of insertion was entered manually into the display of the unit by the interventional radiologist. A prospective multicenter trial was carried out. RESULTS: A mean of 1.1 needle passes were necessary to reach the target, and in 55 (84.6%) of the patients the target was reached on the first needle pass. The mean deviation of the needle from the preselected angle was 1.8 degrees. The mean targeting time (from the initial localizing scan until the needle was in the target) was 15.6 min. In every case, both the usefulness and the ease of use of the laser guidance system were subjectively evaluated on a 5-point scale; the mean usefulness score was 4.5, while the mean ease of use score was 4.7. CONCLUSION: Different users at four different centers found the laser guidance system useful and easy to use. A high level of accuracy of the puncture angle was obtained in most cases.

Adult↗
PubMed2002

Architecture and callosal connections of visual areas 17, 18, 19 and 21 in the ferret (Mustela putorius).

Visual areas 17, 18, 19 and 21 of the ferret can be distinguished on the grounds of cytoarchitecture, myeloarchitecture and cytochrome oxidase reactivity, and with transneuronal tract-tracing from the eye. Each visual area contains callosally connected, as well as acallosal, regions. The callosal connections originate mainly from layers 2 and 3 and, more widely, from layer 6. Callosally projecting neurons and callosal terminals are organized in three roughly medio-laterally oriented bands. The posterior and intermediate bands straddle the 17/18 and 19/21 border, respectively; the third band extends along the medial bank of the lateral suprasylvian sulcus. These bands are linked by a variable number of bridges of connections that demarcate acallosal islands. The distribution of callosal connections predicts the existence of vertical meridian representations corresponding to each of the bands and of non-isotropic representations of the visual field within the bridges and islands.

Animals↗
PubMed2002

Three-lobe-shaped equilibrium states in magnetic liquid bridges.

Stable 3-lobed cross sectional equilibrium shapes, invariant under rotations of 120 degrees, are reported in magnetic liquid drops confined between two horizontal plates in the presence of a vertical dc magnetic field. Their connectivity with other 4-, 3- or 2-lobed shapes as magnetic field strength varies is studied experimentally. Although 3-lobed shapes are found to evolve into bent 2-lobed ones by slowly decreasing the field strength, the reverse transition is not observed when the field strength increases. Moreover, 2-lobed shapes suffer a bending transition, by increasing the field strength, which is found to be hysteretic.

Journal Article↗
PubMed2006

Lateral diffusion and percolation in membranes.

An algorithm based on Voronoi tessellation and percolation theory is presented to study the diffusion of model membrane components (solutes) in the plasma membrane. The membrane is modeled as a two-dimensional space with integral membrane proteins as static obstacles. The Voronoi diagram consists of vertices, which are equidistant from three matrix obstacles, joined by edges. An edge between two vertices is said to be connected if solute particles can pass directly between the two regions. The percolation threshold, pc, determined using this passage criterion is pc approximately equal to 0.53. This is smaller than if the connectivity of edges were assigned randomly, in which case the percolation threshold pr=2/3, where p is the fraction of connected edges. Molecular dynamics simulations show that diffusion is determined by percolation of clusters of edges.

Algorithms↗
PubMed1995

Shape and spatial distribution of receptive fields and antagonistic motion surrounds in the middle temporal area (V5) of the macaque.

The spatial organization of receptive fields in the middle temporal (MT) area of anaesthetized and paralysed macaque monkeys was studied. In all, 288 neurons were successfully recorded. The size and shape of the receptive field (RF) was mapped with small patches of translating random dots and the resulting data were fitted with a generalized Gaussian. Results show that the RF area increases with eccentricity, and is larger in lamina 5 than in other layers. Most of these RFs are elongated, and the axis of elongation tends to be orthogonal to the preferred direction of motion. The direction selectivity is maintained in all positions in the RF, but layer 5 cells are less direction-selective than cells in other layers. In a second series of experiments, radial dimensions of the classical RF and the antagonistic surround were estimated from area summation tests. These data were fitted with the difference of the integrals of two Gaussians. Surrounds were weakest in layer 4 and strongest in layer 2. Optimal stimulus diameters, also estimated from the area summation curve, were larger in the infragranular layers than in the other layers. The maximum sensitivity of the surround was clearly displaced from the classical RF (CRF) centre, indicating that the surround is not concentric with the CRF. This radial offset and the extent of the surround were largest in layers 2 and 5 and smallest in 3a. The extent of the surround half-height equalled, on average, 3-4 times that of the CRF. These results suggest that antagonistic surrounds are constructed in MT, probably through horizontal connections, and that a strong vertical organization exists in area MT, as has been shown for V1.

Animals↗
PubMed2004

Optical coherence tomography in the diagnosis of juvenile X-linked retinoschisis.

PURPOSE: To describe the value of optical coherence tomography (OCT) as a diagnostic tool in the diagnosis of X-linked retinoschisis. METHODS: We report three boys aged between 8 and 17 years, diagnosed with X-linked retinoschisis. During investigations they were examined with OCT (Zeiss Humphrey OCT 1, upgraded version). Single scans of the central posterior pole and the region around the vascular arcades were obtained. Two of the boys underwent full-field ERG according to ISCEV standards. Genetic analysis was performed in all three boys, with sequencing of the XLRS gene. RESULTS: The OCT results revealed a pattern with a cleavage of the retina in two distinct planes, one deep (outer retina) and one superficial. This was very obvious in one patient and a similar but not as pronounced pattern was seen in the other two cases. The two layers were superficially connected with thin-walled, vertical palisades, separated by low reflective, cystoid spaces, confluent and most prominent in the foveal region. CONCLUSION: Full-field ERG and/or DNA analysis are well known methods used for diagnosis of X-linked juvenile retinoschisis. In this paper, we suggest that OCT can also be a helpful diagnostic tool.

Adolescent↗
PubMed1978

The third visual complex of rhesus monkey prestriate cortex.

1. Two independent but neighbouring visual areas, V3 and V3A, sharing a common cytoarchitectural plan, but in each one of which the visual fields are separately represented, have been studied anatomically, functionally, and in combined anatomico-physiological experiments. 2. The properties of single cells in the two areas are so similar, judged by the techniques used in this study, that it is often impossible to tell whether any one penetration was sampling from cells in V3 or V3A. This is especially so if the cells have receptive fields in the lower hemi-quadrants, since the vertical meridian of the lower visual fields is represented along the V3-V3A boundary and since a transition from V3 to V3A along this border is not accompanied by a shift in receptive field positions of cells. 3. Since the visual fields, including the vertical meridian, are separately represented in these two areas, and since regions of vertical meridian representation are callosally connected, a simple and certain method of specifying the boundary between V3 and V3A is to examine the degeneration following section of the callosal splenium. A heavy patch of degeneration then marks the V3-V3A boundary. Within this patch, however, is a sub-patch containing fewer callosal fibres, or none at all. The boundary between V3 and V3A was taken to be at this subpatch. 4. Since the horizontal meridian is represented at the V2-V3 boundary, and since V1 projects to both these areas, sending coarse fibres to V3 and fine fibres to V2, it was found that the boundary between V2 and V3 could be precisely drawn by making a lesion in the horizontal meridian representation in V1 and noting where, in the prestriate cortex, fine fibres give way to coarse ones, without an intervening gap. 5. Double tracer anatomical experiments, in which tritiated proline was injected into V1 of animals whose callosal splenium had been sectioned, showed that whereas V3 receives a direct input from V1, V3A does not. V3A, instead, was found to receive an input from V3. Double tracer anatomical experiments were undertaken to study a possible input from V2 to V3A. Although such experiments did not reveal a direct input from V2 to V3A, they were not entirely conclusive. 6. The vast majority of cells in V3 and V3A were binocularly driven, without obvious monocular preferences. Some cells, however, though responding to stimulation of the individual eyes, summated their responses to binocular stimulation. Others responded only when both eyes were simulataneously stimulated. In any oblique penetration, cells preferring binocular stimulation only occurred either singly or in groups. 7. In an oblique penetration, the shift from a cell responding to binocular stimulation only to one responding equally well to stimulation of either eye was not necessarily accompanied by a shift in orientational preferences, shifts in the former...

Animals↗
PubMed1987

Functional characterization of cell-to-cell coupling in cultured rat aortic smooth muscle.

Gap junction (GJ) occurrence and function was studied in cultured rat aortic smooth muscle cells, since cell-to-cell coupling is proposed to coordinate smooth muscle function but is difficult to study in the intact tissue. Cell proliferation in vitro formed a multilayered structure 10-15 cells thick. GJs connected cells to lateral and vertical neighbors, appearing in freeze fracture as P-face particles aggregated into circular plaques but also as linear arrays. The membrane potential was 58 +/- 3 mV. From quantification of the spread of electrotonic potentials according to a two-dimensional model, the intercellular resistivity was 900-1,400 omega X cm, whereas the nonjunctional membrane resistivity was 10(4) omega X cm2. Intercellular spread of 5(6)-carboxyfluorescein (CF; mol wt 376) in aortic cultures suggests that metabolic coupling is an important consequence of GJs in smooth muscle. CF transfer was not blocked by A23187 (10(-5) M), although rat fibroblasts became uncoupled by 10(-6) M. Ultimately uncoupled by the more potent ionophore ionomycin (10(-5) M), aortic cells seem more able to maintain GJ permeability during challenge from increased intracellular Ca than cells of noncontractile origin.

Animals↗
PubMed1978

New apparatus for exercising a monkey seated in a primate chair.

A new apparatus and method for exercising a monkey seated in a primate chair are described. The apparatus consists of a set of hand and foot bars mounted at either end of a rocker arm that pivots in a vertical plane. This arm is connected by a steel cable to a wooden box that houses lead weights. By simultaneously pushing the foot bar and pulling the hand bar, the monkey lifts a weight and triggers a microswitch which releases a banana-flavored food pellet into a well close to the animal's mouth. The amount of work performed is varied by changing the a) amount of weight to be lifted, b) distance the weight must be lifted, or c) number of times that the animal lifts the weight for a single reward. During 30 min of exercise, the heart rate of a given monkey rose 120 beats/min, respiratory rate 24/min, and colonic temperature 1.2 degrees C above base-line values. Total work performed in 30 min varied from 250 to 360 kpm. Major advantages of this apparatus over a treadmill or bicycle ergometer are that the animal 1) is restrained sufficiently to permit the delicate experimental manipulations and physiological measurements, 2) can be exercised strenuously in a quantitative fashion, and 3) is readily trained to perform the task in a short time.

Animals↗
PubMed1997

Neural mechanisms of reflex reversal in coxo-basipodite depressor motor neurons of the crayfish.

The in vitro preparation of the fifth thoracic ganglion of the crayfish was used to investigate the mechanisms underlying the reflex reversal in a sensory-motor pathway. Sensory afferent neurons from the coxo-basipodite chordotonal organ (CBCO), which senses vertical movements of the limb, connect monosynaptically with basal limb motor neurons (MNs). In tonically active preparation, stretching the CBCO (corresponding to downward movements of the leg) stimulates the levator MNs, whereas releasing the CBCO activates the depressor (Dep) MNs. These reflexes, opposed to the imposed movement, are termed resistance reflexes. By contrast, during fictive locomotion, the reflexes are reversed and termed assistance reflexes. Intracellular recordings from all 12 Dep MNs were performed in single experiments. It allowed us to characterize three types of Dep MNs according to their response to CBCO imposed step-and-ramp movements: 8 of the 12 Dep MNs are resistance MNs that are depolarized during release of the CBCO and are connected monosynaptically to release-sensitive CBCO neurons; 1 Dep MN is an assistance MN that is depolarized during stretching of the CBCO and is connected monosynaptically to exclusively velocity-coding stretch-sensitive CBCO neurons; in our experimental conditions, 3 Dep MNs do not display any response to CBCO stimulation. Assistance reflex interneurons (ARINs), involved in polysynaptic assistance reflexes recorded from depressor MNs, are presented. During low-velocity (0.05 mm/s) stretching ramps imposed on the CBCO, ARINs display compound excitatory postsynaptic potentials (EPSPs), whereas during high-velocity (0.25 mm/s) ramps, they display a mixed excitatory and inhibitory response. Whereas a single MN generally receives monosynaptic EPSPs from three to six CBCO neurons, ARINs receive monosynaptic EPSPs from up to eight velocity-coding stretch-sensitive CBCO neurons. In addition, ARINs receive disynaptic inhibitory phasic inputs from stretch-sensitive CBCO afferents. Injection of a depolarizing current pulse into ARINs elicits a fast transient voltage-dependent depolarization. Its time to peak decreases, and its peak amplitude increases with increasing current intensity. ARINs likely are to be connected directly to Dep MNs. The synaptic delay between these nonspiking ARINs and Dep MNs is short (<2 ms) and constant. The postsynaptic EPSP amplitude increases with increasing current pulse intensity injected into ARIN. The dual sensory control (excitatory and inhibitory) makes it likely that ARIN represents a key element in reflex reversal control.

Adaptation, Physiological↗
PubMed1975

Echocardiographic features of total anomalous pulmonary venous connection.

Seven patients, four months to ten years of age, with total anomalous pulmonary venous connection (TAPVC) were studied by echocardiography. The diagnosis was confirmed by cardiac catheterization, angiography, and surgery in each. The connection was to the left vertical vein in four patients, to the coronary sinus in one, to the inferior vena cava in one, and directly to the right atrium in one. All patients exhibited the echocardiographic criteria of right ventricular diastolic volume overload (RVDVO). In addition, an echo-free space was identified dorsal to the posterior wall of the left atrium. Indocyanine green dye studies done in one of the patients provided evidence that this echo-free space represents the common pulmonary venous chamber. The combination of echocardiographic evidence of RVDVO and demonstration of an echo-free space dorsal to the left atrium is strongly suggestive of TAPVC and should allow an early diagnosis in infants with this anomaly.

Angiocardiography↗
PubMed1990

[The histopathological study of periodontal tissue regeneration using atelocollagen membranes].

In an attempt to promote periodontal tissue regeneration following periodontal surgery, an experimental study was conducted by applying the guided tissue regeneration (GTR) technique to a cross-linked atelocollagen membrane. The palatal gingiva of maxillary first molars of rats were dissected and the cementum was removed by curettage. An atelocollagen membrane was implanted into the site of dissection in the experimental group, while the control group received no implant. The wound healing processes in two groups were examined by histopathological methods, including histometric analysis of the cells and histological measurement of the regenerated periodontal tissue, 1, 3, 5, 7, 14 and 21 days, and 1, 2, 3 and 4 months after the implantation. The results were as follows. 1) Implantation of the atelocollagen membrane did not enhance or prolong the inflammatory reaction, indicating possible involvement of inflammatory cells and macrophages in the membrane absorption. 2) In the experimental group, epithelial downgrowth was markedly inhibited and fiber bundles of the gingival connective tissue were clearly arranged vertical to the root surface. 3) The experimental group showed a significant increase in new cementum formation 2 months after surgery compared with the control group. Root resorption was seldom observed in either group during the study period. The above results indicate that the GTR technique using an atelocollagen membrane may provide an effective method to promote periodontal tissue regeneration after periodontal surgery.

Animals↗
PubMed1993

Computer networks.

We have looked at several aspects of networks in this article. As you read about networks, and use them, we hope our discussions will help you understand some of the associated concepts and terms. For instance, suppose someone describes an Ethernet installation as a bus topology LAN using the 1-persistent CSMA/CD protocol with horizontal cables on each floor connected by repeaters to a vertical cable backbone running from the basement to the roof. You now have seen what that description implies. To close this article, we ask you to refer back to Figure 1. Our sample network transfer from Marie to Lars was described as being accomplished through a number of layers or steps, most of which were transparent to the users. Building upon the material presented in this article, we can now give you a more detailed illustration of those layers. Figure 13 shows the seven layers in network model defined by the International Standards Organization, ISO: application, presentation, session, transport, network, data link, and physical. We do not have space here to discuss each layer in detail, but Figure 13 does give a typical operation that is done in each layer.

Computer Communication Networks↗
PubMed2004

[Surgical anatomy of transoral atlantoaxial reduction plate internal fixation].

OBJECTIVE: To provide anatomical data for transoral atlantoaxial reduction plate internal fixation. METHOD: Microsurgical dissecting was performed on 10 fresh craniocervical specimens layer by layer according to transoral approach. Stratification of posterior pharyngeal wall, course of vertebral artery, adjacent relationships of atlas and axis and correlative anatomical parameters of internal fixation to atlantoaxial joint were observed. RESULT: (1) Posterior pharyngeal wall consisted of 2 layers and 2 interspace: mucosa, anterior fascia of vertebrae, posterior interspace of pharynx and anterior interspace of vertebrae. (2) The range from anterior rim of foramen magnum to C3 could be exposed by this approach. (3) The distance between the vertebral artery at atlas and midline was (25.2 +/- 2.3) mm and that between the vertebral artery at axis and midline was (18.4 +/- 2.6) mm. (4) The width of atlas and that of axis could be exposed respectively to (39.4 +/- 2.2) mm and (39.0 +/- 2.1) mm. The distance (a) between 2 atlas screw inserting points (center of anterior aspect of C-1 lateral mass) was (31.4 +/- 3.3) mm. The vertical distance (b) between the connecting line of 2 atlas screw inserting points and that of 2 axis screw inserting points (at the central part of the vertebrae which was 3 - 4 mm lateral to the midline of C-2 vertebrae) was (18.7 +/- 2.7) mm. The odds of a/b was 1.5 approximately 1.7. CONCLUSIONS: Anterior atlantoaxial plate internal fixation through transoral approach is suitable and feasible. The design of the plate should be based on the above data.

Atlanto-Occipital Joint↗
PubMed1991

[The meaning of taurodontism in oral surgery--case report].

Taurodontism represents morphological abnormality of the teeth followed by the enlargement of the elongation of the pulp chamber in vertical direction; and which is connected with: racial traits, some syndromes, or in most cases appears as the consequence of the increased number of X chromosomes. In the study is presented rare case of hypertaurodont maxillary second premolar and surgical admission during the extraction. Since the classical extraction was not possible because of the rooth mass and the alveol wideness, we did the alveotomia.

Alveolectomy↗
PubMed1989

Evidence of differential growth in the human skull from sagittal and transversal deviations of landmarks.

The differences in position along, and deviations from the midline of six landmarks on the base and face of 51 recent skulls of recorded sex and age from Middle Europe were studied. There is accordance between the average anatomical position of the landmarks and their mean vertical distances from the line connecting the two poria. The majority of the specimens show deviations from the midline predominantly towards the left half of the skull. Variation of the landmarks is discussed with respect to differing growth processes and with respect to the frequently asymmetric location of the two poria cited in the literature.

Adult↗
PubMed1989

[Dynamic age-related changes in the human physique at stages in postnatal development].

In 926 children (7 age groups) combined group differences of the signs have been studied by means of a unified standardized method, using the hand length as a linear measure; the conformity index to definitive size has been applied. For newborns proportional discrepancy to the definitive sizes is specific. They have a relatively long, thick and round body, short extremities, large dimensions of the head and abundant adipose subcutaneous deposits. According to the constitutional peculiarities the newborns resemble the children of the digestive type in mature persons--pycnotic or endomorphic. Beginning from birth, including children of early and first childhood (4-7 years of age), age changes of complexion go in two directions: a) dolichomorphy of complexion is realized; for it decreasing diameters of the chest and dimensions of the neck, chest, abdomen, pelvis (in boys), shoulder, arm, hand, foot and decrease in the subcutaneous adipose tissue are specific; b) longitudinal proportions of body and extremity segments change under influence of biomechanical adaptations to physical loads in connection with adaptation to the vertical position.

Adolescent↗